Lithographic apparatus and device manufacturing method

ABSTRACT

An immersion lithography apparatus includes a liquid supply system configured to supply a liquid to a space through which a beam of radiation passes, the liquid having an optical property that can be tuned by a tuner. The space may be located between the projection system and the substrate. The tuner is arranged to adjust one or more properties of the liquid such as the shape, composition, refractive index and/or absorptivity as a function of space and/or time in order to change the imaging performance of the lithography apparatus.

The present application is a continuation of co-pending U.S. patentapplication Ser. No. 12/230,979, filed on Sep. 9, 2008, now allowed,which is a continuation of U.S. patent application Ser. No. 10/961,369,filed on Oct. 12, 2004, now U.S. Pat. No. 7,433,015, which claimspriority to European Patent Application No. EP 03256499.9, filed Oct.15, 2003, the entire contents of each of the foregoing applicationsherein fully incorporated by reference.

FIELD

The present invention relates to a lithographic projection apparatus anda device manufacturing method.

BACKGROUND

The term “patterning device” as here employed should be broadlyinterpreted as referring to any device that can be used to endow anincoming radiation beam with a patterned cross-section, corresponding toa pattern that is to be created in a target portion of the substrate;the term “light valve” can also be used in this context. Generally, thepattern will correspond to a particular functional layer in a devicebeing created in the target portion, such as an integrated circuit orother device (see below). Examples of such a patterning device include:

A mask. The concept of a mask is well known in lithography, and itincludes mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. Placementof such a mask in the radiation beam causes selective transmission (inthe case of a transmissive mask) or reflection (in the case of areflective mask) of the radiation impinging on the mask, according tothe pattern on the mask. In the case of a mask, the support structurewill generally be a mask table, which ensures that the mask can be heldat a desired position in the incoming radiation beam, and that it can bemoved relative to the beam if so desired.

A programmable mirror array. One example of such a device is amatrix-addressable surface having a viscoelastic control layer and areflective surface. The basic principle behind such an apparatus is that(for example) addressed areas of the reflective surface reflect incidentlight as diffracted light, whereas unaddressed areas reflect incidentlight as undiffracted light. Using an appropriate filter, theundiffracted light can be filtered out of the reflected beam, leavingonly the diffracted light behind; in this manner, the beam becomespatterned according to the addressing pattern of the matrix-addressablesurface. An alternative embodiment of a programmable mirror arrayemploys a matrix arrangement of tiny mirrors, each of which can beindividually tilted about an axis by applying a suitable localizedelectric field, or by employing piezoelectric actuation means. Onceagain, the mirrors are matrix-addressable, such that addressed mirrorswill reflect an incoming radiation beam in a different direction tounaddressed mirrors; in this manner, the reflected beam is patternedaccording to the addressing pattern of the matrix-addressable mirrors.The required matrix addressing can be performed using suitableelectronic means. In both of the situations described hereabove, thepatterning device can comprise one or more programmable mirror arrays.More information on mirror arrays as here referred to can be gleaned,for example, from U.S. Pat. Nos. 5,296,891 and 5,523,193, and PCT patentapplications WO 98/38597 and WO 98/33096, which are incorporated hereinby reference. In the case of a programmable mirror array, the supportstructure may be embodied as a frame or table, for example, which may befixed or movable as required.

A programmable LCD array. An example of such a construction is given inU.S. Pat. No. 5,229,872, which is incorporated herein by reference. Asabove, the support structure in this case may be embodied as a frame ortable, for example, which may be fixed or movable as required.

For purposes of simplicity, the rest of this text may, at certainlocations, specifically direct itself to examples involving a mask andmask table; however, the general principles discussed in such instancesshould be seen in the broader context of the patterning device ashereabove set forth.

Lithographic projection apparatus can be used, for example, in themanufacture of integrated circuits (ICs). In such a case, the patterningdevice may generate a circuit pattern corresponding to an individuallayer of the IC, and this pattern can be imaged onto a target portion(e.g. comprising one or more dies) on a substrate (silicon wafer) thathas been coated with a layer of radiation-sensitive material (resist).In general, a single wafer will contain a whole network of adjacenttarget portions that are successively irradiated via the projectionsystem, one at a time. In current apparatus, employing patterning by amask on a mask table, a distinction can be made between two differenttypes of machine. In one type of lithographic projection apparatus, eachtarget portion is irradiated by exposing the entire mask pattern ontothe target portion at one time; such an apparatus is commonly referredto as a stepper. In an alternative apparatus—commonly referred to as astep-and-scan apparatus—each target portion is irradiated byprogressively scanning the mask pattern under the projection beam in agiven reference direction (the “scanning” direction) while synchronouslyscanning the substrate table parallel or anti-parallel to thisdirection; since, in general, the projection system will have amagnification factor M (generally <1), the speed V at which thesubstrate table is scanned will be a factor M times that at which themask table is scanned. More information with regard to lithographicdevices as here described can be gleaned, for example, from U.S. Pat.No. 6,046,792, incorporated herein by reference.

In a manufacturing process using a lithographic projection apparatus, apattern (e.g. in a mask) is imaged onto a substrate that is at leastpartially covered by a layer of radiation-sensitive material (resist).Prior to this imaging step, the substrate may undergo variousprocedures, such as priming, resist coating and a soft bake. Afterexposure, the substrate may be subjected to other procedures, such as apost-exposure bake (PEB), development, a hard bake andmeasurement/inspection of the imaged features. This array of proceduresis used as a basis to pattern an individual layer of a device, e.g. anIC. Such a patterned layer may then undergo various processes such asetching, ion-implantation (doping), metallization, oxidation,chemo-mechanical polishing, etc., all intended to finish off anindividual layer. If several layers are required, then the wholeprocedure, or a variant thereof, will have to be repeated for each newlayer. Eventually, an array of devices will be present on the substrate(wafer). These devices are then separated from one another by atechnique such as dicing or sawing, whence the individual devices can bemounted on a carrier, connected to pins, etc. Further informationregarding such processes can be obtained, for example, from the book“Microchip Fabrication: A Practical Guide to Semiconductor Processing”,Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN0-07-067250-4, incorporated herein by reference. For the sake ofsimplicity, the projection system may hereinafter be referred to as the“projection lens”; however, this term should be broadly interpreted asencompassing various types of projection system, including refractiveoptics, reflective optics, and catadioptric systems, for example. Theradiation system and projection system may include components operatingaccording to any of these design types for directing, shaping orcontrolling the projection beam of radiation, and such components mayalso be referred to below, collectively or singularly, as a “lens”.Further, the lithographic apparatus may be of a type having two or moresubstrate tables (and/or two or more mask tables). In such “multiplestage” devices the additional tables may be used in parallel, orpreparatory steps may be carried out on one or more tables while one ormore other tables are being used for exposures. Dual stage lithographicapparatus are described, for example, in U.S. Pat. No. 5,969,441 and PCTpatent application WO 98/40791, incorporated herein by reference.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.)

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate (the substrategenerally has a larger surface area than the final element of theprojection system). One way which has been proposed to arrange for thisis disclosed in PCT patent application WO 99/49504, hereby incorporatedin its entirety by reference. As illustrated in FIGS. 2 and 3, liquid issupplied by at least one inlet IN onto the substrate, preferably alongthe direction of movement of the substrate relative to the finalelement, and is removed by at least one outlet OUT after having passedunder the projection system. That is, as the substrate is scannedbeneath the element in a −X direction, liquid is supplied at the +X sideof the element and taken up at the −X side. FIG. 2 shows the arrangementschematically in which liquid is supplied via inlet IN and is taken upon the other side of the element by outlet OUT which is connected to alow pressure source. In the illustration of FIG. 2 the liquid issupplied along the direction of movement of the substrate relative tothe final element, though this does not need to be the case. Variousorientations and numbers of in- and outlets positioned around the finalelement are possible, one example is illustrated in FIG. 3 in which foursets of an inlet with an outlet on either side are provided in a regularpattern around the final element.

SUMMARY

As system resolution is improved, it becomes increasingly difficult andexpensive to control lens aberrations and focus. The introduction of animmersion liquid in an immersion lithography apparatus has made the taskmore difficult because the optical properties of the liquid are complexand sensitive to small variations in temperature and contaminantconcentration, both of which may change with time and position.

Accordingly, it would be advantageous, for example, to control moreefficiently the optical performance of an immersion lithographyprojection system.

According to an aspect of the invention, there is provided alithographic projection apparatus, comprising:

an illumination system configured to condition beam of radiation;

a support structure configured to hold a patterning device, thepatterning device configured to pattern the beam of radiation accordingto a desired pattern;

a substrate table configured to hold a substrate;

a projection system configured to project the patterned beam onto atarget portion of the substrate;

a liquid supply system configured to supply a liquid to a space throughwhich the beam of radiation passes, the liquid having an opticalproperty that can be tuned; and

a tuner configured tune the optical property.

Imaging radiation may be influenced by one or more portions of liquidencountered prior to the substrate. By providing a tuner to tune one ormore optical properties of these one or more portions and, in anembodiment, use them as a liquid lens(es), it is possible to achieveflexible and dynamic control over imaging performance of thelithographic apparatus. The nature of liquid allows tuning modes thatare not possible with a conventional solid lens or other opticalelement.

An embodiment of the invention may be applied to both immersion andnon-immersion lithographic projection apparatus. Where an embodimentrelates to an immersion lithographic apparatus, the liquid supply systemof the apparatus may configured to at least partly fill a space betweenthe projection system and the substrate with a liquid, and the opticalproperty of the liquid in that space may be tuned. An advantage of usingthe liquid in the space between the projection system and the substrateis that no new volume of liquid needs to be introduced into theapparatus. Additionally, one or more optical properties of that liquidare brought under control, thus removing a need for extensiveadjustments to the projection system to allow for that liquid. As anexemplary embodiment, the liquid may be used to compensate for one ormore specific problems in the projection system. This approach has anadvantage of reducing the need for complex and costly features such asinternal lens manipulators (e.g. Z-manipulators, ALE-manipulators),which might otherwise be required to tune the projection system. Wheresuch lens manipulators are still required, an embodiment of the presentinvention may reduce the range through which they are required tooperate. The liquid may also provide an alternative to using calciumfluoride (CaF₂) for image/lens color correction.

The tuner may be arranged to control spatial dependence of the opticalproperty of the liquid in the space, creating an uniform offset orspatially varying optical property profile. One or more anamorphicimaging effects (e.g. astigmatism offset, asymmetric lens magnification)may be compensated by creating an anamorphic optical property profile(i.e. a profile wherein an optical property is different along twoorthogonal directions). This configuration can be used to compensate alens heating induced effect.

The tuner may be arranged to provide and control a time-varying opticalproperty of the liquid in the space. Changing a temperature profile withtime, for example, coordinated with scanning movement of the substraterelative to the projection system, can induce a lateral refractive indexvariation which can be used to compensate image tilt/curvature and/ordistortion effects.

The tuner may comprise a liquid temperature controller configured tocontrol a temperature profile, and thereby one or more propertiesincluding a refractive index profile, an absorptivity profile, or both,of the liquid in the space. The refractive index profile affects thepath the radiation takes through the liquid and can thus be used tocontrol one or more geometric features of the image such as focus and/oraberration. Temperature provides a highly flexible means of control.Controlling the temperature profile may also affect one or more dynamicproperties of the liquid by influencing viscosity and/or by introducingconvective currents.

The temperature controller may comprise one or more heat exchangersconfigured to establish a homogeneous or non-uniform temperature profilewithin the liquid in the space. Each heat exchanger can act to add heatto the liquid or to remove heat from the liquid.

In an embodiment, the temperature controller may comprise a plurality ofindependent heat exchangers arranged at different heights, radii and/orangles relative to an axis lying in a plane substantially parallel tothe substrate.

The one or more heat exchangers may be arranged to add heat to or removeheat from, but not exchange liquid with, the liquid in the space. One ormore heat exchangers thus arranged may comprise an element which isimmersed in the liquid and maintained at a temperature higher or lowerthan that of the liquid according to whether or not it is requiredrespectively to add or remove heat.

In an embodiment, the one or more heat exchangers may be arranged to addheat to or remove heat from, and exchange temperature conditioned liquidwith, the liquid in the space. One or more heat exchangers that do notexchange liquid with the liquid in the space rely on thermal conductionand convection currents to transport heat, which may lead to delays andunpredictability. By designing the one or more heat exchangers to createcurrents of temperature controlled liquid, the temperature profile maybe adjusted more quickly and accurately. As an exemplary embodiment, theone or more heat exchangers may be arranged in pairs, with a firstelement of each pair adding temperature conditioned liquid and a secondelement removing liquid. Each pair may further be arranged to be alignedin a plane substantially parallel to the plane of the substrate. In thisway, more efficient heat transfer may be achieved. In addition, anuniform controlled flow of liquid substantially parallel to thesubstrate may be provided that allows more predictable and homogeneousoptical properties by reducing convection currents, turbulence and thelike.

The one or more heat exchangers may be coupled with the liquid supplysystem for effecting the exchange of temperature conditioned liquid.This arrangement may be cost effective from a manufacturing perspectivesince the liquid supply system may already be arranged to supply acontrolled flow of liquid, for example, to a space between theprojection system and the substrate.

The tuner may comprise a liquid pressure controller configured tocontrol the pressure, and thereby one or more properties including therefractive index and/or absorptivity, of the liquid in the space. Theuse of pressure has an advantage of high stability and predictability.

The tuner may comprise a liquid geometry controller configured tocontrol a shape of the liquid in the space. The liquid geometrycontroller may operate in combination with the liquid pressurecontroller to vary one or more imaging properties of the liquid. Varyingthe shape of the liquid in the space in this manner allows flexibletuning and may provide a highly stable liquid lens environment.

The liquid geometry controller may control the thickness of the liquidin the space in a direction substantially parallel to the axis of afinal element of the projection system. Increasing the relativethickness of the liquid in this way may be used to control sphericalaberration, for example. This mode has an advantage of providing anadditional means to compensate spherical aberration offset, which cannormally be adjusted only over a limited range. For example,Z-manipulators eventually cause cross talk to other aberrations.

The tuner may comprise a liquid composition controller configured tocontrol the composition, and thereby one or more properties includingthe refractive index and/or absorptivity, of the liquid in the space.

The liquid composition controller may comprise one or more particleexchangers configured to add impurity ions to and/or remove impurityions from the liquid in the space. The liquid composition controller maybe coupled with the liquid supply system to provide one or more purityconditioned influxes of liquid.

The liquid composition controller may be arranged to replace a firstliquid in the space with a second liquid of different composition.Water, ethanol, acetone and benzoate are examples of substances that maybe used for either of the first or second liquids. In an embodiment,completely refreshing the liquid in the space provides increased controland scope for image manipulation.

The lithographic projection apparatus may further comprise one or moreliquid sensors configured to measure, as a function of position and/ortime, a property of the liquid in the space including any one or more ofthe following: temperature, pressure, boundary geometry, composition,refractive index and absorptivity. Additionally, the apparatus maycomprise a device configured to correct the focus of the apparatus as afunction of the refractive index profile of the liquid in the space, asmeasured by the one or more liquid sensors. A variation in focus issignificantly dependent on a variation of the refractive index of theliquid. By concentrating on a significant physical property, this devicemay improve the efficiency with which focus in the lithographicapparatus may be controlled.

In an embodiment, the apparatus may comprise a device configured tocorrect an exposure dose of the apparatus as a function of theabsorptivity profile of the liquid in the space, as measured by the oneor more liquid sensors. A variation in radiation intensity reaching thesubstrate is significantly dependent on a variation in the absorptivityof the liquid. By concentrating on a significant physical property, thisdevice may improve the efficiency with which exposure dose in thelithographic apparatus may be controlled

An approach of adjusting one or more optical properties of theprojection system to compensate for a liquid in a space between theprojection system and the substrate without making reference to in situmeasurement of one or more properties of the liquid, requiresexploration of a large parameter space and may therefore be timeconsuming and costly. Liquids for immersion lithography typically havevarious physical properties, including dynamic ones caused by systemflow and convection, that each influence the optical performance indifferent ways. According to an embodiment of the invention when appliedto a liquid in a space between the projection system and the substrate,combining in situ measurement of one or more liquid properties with aknowledge of how each property influences a particular aspect of theoptical performance of the projection system allows more efficienttuning of the projection system.

The tuner may be arranged to create an optical effect includingspherical aberration and/or field curvature. This feature may be used tocompensate for spherical aberration and/or field curvature originatingin the projection system, and thus obviate the need for additionalinternal lens manipulators or other adjustment devices.

The tuner may comprise a computer controller configured to calculate therequired size of correction to one or more optical properties of theprojection system and/or the liquid based on a measured property. Thisapproach obviates the need for extensive experimental tests to determinehow the system may respond to adjustment of a refractive index and/orabsorptivity profile. The computer controller may obtain an estimate forsuch a response via a computer model of the projection system and theliquid (which may or may not be simplified) that provides exact ornumerical solution of relevant physical equations

According to a further aspect of the invention, there is provided adevice manufacturing method, comprising:

providing a liquid in a space through which a beam of radiation passes;

tuning an optical property of the liquid in the space; and

projecting the beam of radiation as patterned by a patterning deviceonto a target portion of a substrate.

According to an aspect of the invention, there is provided alithographic projection apparatus, comprising:

an illumination system configured to condition beam of radiation;

a support structure configured to hold a patterning device, thepatterning device configured to pattern the beam of radiation accordingto a desired pattern;

a substrate table configured to hold a substrate;

a projection system configured to project the patterned beam onto atarget portion of the substrate;

a lens formed from a liquid and having an optical property that can betuned; and

a tuner configured tune the optical property.

Although specific reference may be made in this text to the use of theapparatus according to the invention in the manufacture of ICs, itshould be explicitly understood that such an apparatus has many otherpossible applications. For example, it may be employed in themanufacture of integrated optical systems, guidance and detectionpatterns for magnetic domain memories, liquid-crystal display panels,thin-film magnetic heads, etc. The skilled artisan will appreciate that,in the context of such alternative applications, any use of the terms“reticle”, “wafer” or “die” in this text should be considered as beingreplaced by the more general terms “mask”, “substrate” and “targetportion”, respectively.

In the present document, the terms “radiation” and “beam” are used toencompass all types of electromagnetic radiation, including ultravioletradiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm).

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic projection apparatus according to anembodiment of the invention;

FIG. 2 depicts a liquid supply system for supplying liquid to the areaaround the final element of the projection system according to anembodiment of the invention;

FIG. 3 depicts the arrangement of inlets and outlets of the liquidsupply system of FIG. 2 around the final element of the projectionsystem according to an embodiment of the invention;

FIG. 4 depicts a projection apparatus comprising a temperature profilecontroller according to an embodiment of the invention;

FIG. 5 depicts a projection apparatus comprising a liquid compositioncontroller according to an embodiment of the invention;

FIG. 6 depicts a projection apparatus comprising a refractive indexmeasurement device configured to measure the refractive index profile ofthe immersion liquid according to an embodiment of the invention;

FIG. 7 depicts a schematic arrangement for the refractive index sensorof FIG. 6;

FIG. 8 depicts a projection apparatus comprising an absorptivitymeasurement device configured to measure the absorptivity profile of theimmersion liquid according to an embodiment of the invention;

FIG. 9 depicts a schematic arrangement for an absorptivity sensoraccording to an embodiment of the invention;

FIG. 10 depicts a projection apparatus comprising liquid pressure andliquid geometry controllers according to an embodiment of the invention;

FIG. 11 depicts a liquid lens comprising a planar pellicle according toan embodiment of the invention;

FIG. 12 depicts a liquid lens comprising a deformed constrained pellicleaccording to an embodiment of the invention; and

FIG. 13 depicts a liquid lens wherein the liquid is contained betweentwo pellicles according to an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic projection apparatusaccording to a particular embodiment of the invention. The apparatuscomprises:

a radiation system Ex, IL, configured to supply a projection beam PB ofradiation (e.g. DUV radiation), which in this particular case alsocomprises a radiation source LA;

a first object table (mask table) MT provided with a mask holderconfigured to hold a mask MA (e.g. a reticle), and connected to a firstpositioner configured to accurately position the mask with respect toitem PL;

a second object table (substrate table) WT provided with a substrateholder configured to hold a substrate W (e.g. a resist-coated siliconwafer), and connected to a second positioner configured to accuratelyposition the substrate with respect to item PL;

a projection system (“projection lens”) PL (e.g. a refractive system)configured to image an irradiated portion of the mask MA onto a targetportion C (e.g. comprising one or more dies) of the substrate W.

As here depicted, the apparatus is of a transmissive type (e.g. has atransmissive mask).However, in general, it may also be of a reflective type, for example(e.g. with a reflective mask). Alternatively, the apparatus may employanother kind of patterning device, such as a programmable mirror arrayof a type as referred to above.

The source LA (e.g. an excimer laser) produces a beam of radiation. Thisbeam is, fed into an illumination system (illuminator) IL, eitherdirectly or after having traversed conditioning means, such as a beamexpander Ex, for example. The illuminator IL may comprise adjustingmeans AM for setting the outer and/or inner radial extent (commonlyreferred to as σ-outer and σ-inner, respectively) of the intensitydistribution in the beam. In addition, it will generally comprisevarious other components, such as an integrator IN and a condenser CO.In this way, the beam PB impinging on the mask MA has a desireduniformity and intensity distribution in its cross-section.

It should be noted with regard to FIG. 1 that the source LA may bewithin the housing of the lithographic projection apparatus (as is oftenthe case when the source LA is a mercury lamp, for example), but that itmay also be remote from the lithographic projection apparatus, theradiation beam which it produces being led into the apparatus (e.g. withthe aid of suitable directing mirrors); this latter scenario is oftenthe case when the source LA is an excimer laser. The current inventionand claims encompass both of these scenarios.

The beam PB subsequently intercepts the mask MA, which is held on a masktable MT. Having traversed the mask MA, the beam PB passes through theprojection system PL, which focuses the beam PB onto a target portion Cof the substrate W. With the aid of the second positioner (and aninterferometric measuring device IF), the substrate table WT can bemoved accurately, e.g. so as to position different target portions C inthe path of the beam PB. Similarly, the first positioner can be used toaccurately position the mask MA with respect to the path of the beam PB,e.g. after mechanical retrieval of the mask MA from a mask library, orduring a scan. In general, movement of the object tables MT, WT will berealized with the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which are not explicitlydepicted in FIG. 1. However, in the case of a stepper (as opposed to astep-and-scan apparatus) the mask table MT may just be connected to ashort stroke actuator, or may be fixed.

The depicted apparatus can be used in two different modes:

1. In step mode, the mask table MT is kept essentially stationary, andan entire mask image is projected at one time (i.e. a single “flash”)onto a target portion C. The substrate table WT is then shifted in the Xand/or Y directions so that a different target portion C can beirradiated by the beam PB;2. In scan mode, essentially the same scenario applies, except that agiven target portion C is not exposed in a single “flash”. Instead, themask table MT is movable in a given direction (the so-called “scandirection”, e.g. the Y direction) with a speed v, so that the projectionbeam PB is caused to scan over a mask image; concurrently, the substratetable WT is simultaneously moved in the same or opposite direction at aspeed V=Mv, in which M is the magnification of the projection system PL(typically, M=¼ or ⅕). In this manner, a relatively large target portionC can be exposed, without having to compromise on resolution.

FIGS. 2 and 3 depict a liquid supply system according to an embodimentof the invention and have been described above. Another liquid supplysystem solution according to an embodiment of the invention is a liquidsupply system with a seal member which extends along at least a part ofa boundary of the space between the final element of the projectionsystem and the substrate table. The seal member is substantiallystationary relative to the projection system in the XY plane thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). A seal is formed between the seal member and thesurface of the substrate. In an embodiment, the seal is a contactlessseal such as a gas seal. Such a system is disclosed in U.S. patentapplication Ser. No. 10/705,783, hereby incorporated in its entirety byreference. Other liquid supply systems may be employed according toembodiments of the invention including, without limitation, a bath ofliquid.

FIGS. 4 to 10 show a liquid in a space through which a beam of radiationpasses according to embodiments of the invention in which an immersionliquid, used for immersion lithography, is used as the liquid. In anembodiment, the liquid in the space forms a liquid lens. A liquid supplysystem supplies liquid to an imaging-field reservoir 12 between theprojection system PL and the substrate W. In an embodiment, the liquidis chosen to have a refractive index substantially greater than 1,meaning that the wavelength of the projection beam is shorter in theliquid than in air or a vacuum, allowing smaller features to beresolved. It is well known that the resolution of a projection system isdetermined, inter alia, by the wavelength of the projection beam and thenumerical aperture of the system. The presence of the liquid may also beregarded as increasing the effective numerical aperture.

The reservoir 12 is bounded at least in part by a seal member 13positioned below and surrounding the final element of the projectionsystem PL. The seal member 13 extends a little above the final elementof the projection system PL and the liquid level rises above the bottomend of the final element of the projection system PL. The seal member 13has an inner periphery that at the upper end closely conforms to thestep of the projection system or the final element thereof and may,e.g., be round. At the bottom, the inner periphery closely conforms tothe shape of the image field, e.g. rectangular but may be any shape.

Between the seal member 13 and the substrate W, the liquid can beconfined to the reservoir by a contact-less seal 14, such as a gas sealformed by gas provided under pressure to the gap between the seal member13 and the substrate W. The liquid may be arranged to be circulated orremain stagnant.

FIG. 4 illustrates an embodiment of the invention in which a tunercomprises a temperature profile controller 24. The temperature profileof the liquid influences predominantly the refractive index profile butlocalized heating/cooling may also influence properties such asabsorptivity and viscosity. The temperature profile controller 24 maycomprise an array of heat exchangers (22,23), which are capable ofheating or cooling the liquid. The heat exchangers may work by contactmeans only (acting locally), or act to supply a flow of temperatureconditioned liquid. In the example shown in FIG. 4, an array of heatexchangers (22,23) provides temperature conditioned liquid via inlets 22and outlets 23 arranged in pairs. Liquid may be made to circulate in aclosed circuit 26 from temperature profile controller 24 through heatexchanger inlets 22 into the reservoir 12 and then back into the closedcircuit 26 via the heat exchanger outlets 23.

The result in this embodiment is a horizontal flow of temperatureconditioned liquid that may support axial (i.e. parallel to the axis ofthe final element of the projection system PL) temperature gradientswith reduced convection currents. The arrangement shown is appropriatefor maintaining such axial temperature gradients. However, radial (froman extension of the axis of the final element of the projection systemPL) temperature gradients may be created or controlled via an analogousarrangement of heat exchangers arranged at different radii, and morecomplex currents may be handled by locating inlets and outlets atdifferent azimuthal angles (i.e. angles relative to a fixed direction ina plane parallel to the substrate W). It is also possible to provide atime-varying temperature profile. This may be done in cooperation withscanning movements of the substrate W and a lateral refractive index canbe induced, along with accompanying image tilt/curvature and distortioneffects.

The inlets 22 and outlets 23 may be coupled with a liquid supply systemsuch as that depicted in FIG. 3. In this example, four groups of ductsare arranged, each angularly spaced from its neighbors by 90°. However,any number of ducts (inlets/outlets) may be used at varioustemperatures, pressures, heights and angular positions for the purposesof tuning one or more optical properties of the immersion liquid.

FIG. 5 shows a further embodiment wherein the tuner comprises a liquidcomposition controller 30. The liquid composition controller 30 may addor remove impurity ions from the immersion liquid in order to influenceproperties such as the refractive index profile or absorptivity. In theexample shown, a single particle exchanger 28 is shown but a pluralityof particle exchangers 28 may be arranged around the reservoir 12 if itis required to create impurity concentration gradients. Additionally oralternatively, one or more particle exchangers 28 may be arranged tocontrol impurities that arise predominantly from particular areas of thereservoir 12 boundary, such as near the substrate W. Again, as for thetemperature profile controller 24, the liquid composition controller 30may be coupled with a liquid supply system such as that depicted in FIG.3.

Additionally or alternatively, a liquid of a different composition maybe added. The second liquid may be mixed with liquid already in thespace or be arranged to replace the original liquid. Examples of liquidsthat may be used include: water, ethanol, acetone and benzoate.

In each case herein, the operation of the tuner may be controlled by acomputer 20 that calculates the required change in the physicalparameter in question via an abstract computer model of the projectionapparatus.

The tuner may be used to create spherical aberration and/or fieldcurvature effects in the liquid in the space. Refractive index changesof between several ppm (parts/million) and several hundred ppm may beused to create such effect(s). For water at 22° C., the rate of changeof refractive index with temperature, dn/dT, is 100 ppm/K. Therefore,changing the refractive index in steps of 50 ppm would requiretemperature steps of 0.5 K. For a typical lens design (variations wouldbe expected between systems of different numerical aperture), this wouldresult in 10-20 nm focus steps and about 1 nm Z9 spherical aberration.The influence of contamination will typically yield approximately 1 ppmchange in refractive index for a 1 ppm change in impurity concentration.For acetone in water the effect is stronger, with an index changemeasured at 10 ppm for a 1 ppm addition of acetone.

FIG. 6 depicts a projection apparatus comprising a measurement device 2configured to measure the refractive index profile of the liquidaccording to an embodiment of the invention. Refractive index sensors16, connected to the device 2, are arranged around the sides of theliquid reservoir 12. Such an arrangement is advantageous where the axialvariation in refractive index is required. The radial variation may bedetermined by positioning sensors 16 at different radii. Sensors thatmeasure through the projection system be used for this purpose.

FIG. 7 shows a schematic arrangement for a refractive index sensor 16.Small quantities of liquid are extracted from the reservoir 12 via thetesting inlet 1 to fill a testing chamber 3. Well collimated light froma light source 5 is arranged to pass through a control medium 7 of knownrefractive index at a fixed angle to the interface between the controlmedium reservoir 9 and the testing chamber 3. The light source 5 may bea low power laser, for example. Light passes through the control medium7 and the immersion liquid in the chamber 3 and is detected by aposition sensitive optical sensor 11 (see example beam path 15). Theangle to the normal is calculated and the refractive index extractedusing Snell's Law.

FIG. 8 depicts a projection apparatus comprising a measurement device 4configured to measure the absorptivity profile of the liquid accordingto an embodiment of the invention. Absorptivity sensors 18 are arrangedin a pairwise fashion around the sides of the liquid reservoir 12 withone element of each sensor pair acting as transmitter and the other as areceiver. The sensors are arranged to be level with each other (in aplane substantially parallel to that of the substrate). The absorptivityis derived by measuring the light attenuation due to propagation acrossthe reservoir 12 of a light beam directed from the transmitter of asensor pair 18 to the matching receiver of the sensor pair 18. Thearrangement depicted is appropriate for measuring axial variations inthe absorptivity profile and for establishing the average overallabsorptivity. Sensors 18 may be arranged at different radii to measureany radial dependence in the absorptivity and/or arranged to measurethrough the projection system.

The absorptivity may also be measured by individual sensors, whichallows more localized measurements of the absorptivity. FIG. 9 depictsan arrangement for such a sensor 32. Here, a small quantity of immersionliquid is removed from the reservoir 12 into an absorptivity testingchamber 34. The absorptivity is derived by monitoring signal attenuationbetween a transmitter 36 and receiver 38.

The measurement device 2, 4 may also comprise one or more sensorsconfigured to measure primary properties such as pressure, temperature,boundary geometry and/or composition. Calibration of one or more ofthese properties may be carried out by reference to sensors forming partof the lithographic apparatus (e.g. focus, aberration and/or dosesensors). Focus, aberration and/or dose sensors may be integrated into awet substrate stage. However, in order to generate useful information,optical measurements using these sensors have to be performed at theimaging wavelength. Therefore, in an embodiment, such measurements aremade offline (i.e. not during imaging) so as not to create strayradiation that could damage the image.

In those sensors described above that extract immersion liquid from thereservoir 12, a mechanism may also be included to purge and replenishthe liquid sample.

In FIGS. 6 and 8, the refractive index measurement device 2 andabsorptivity measurement device 4 are coupled respectively to one ormore devices configured to correct the focus 8 and/or exposure dose 10of the projection apparatus via a computer 20. The computer 20calculates, based on the measured property(ies), what changes to thefocus and/or exposure dose need to be made. This calculation may becarried out based on a feedback mechanism, with a PID(proportional-integral-differential) controller to ensure optimalconvergence of the focus and/or exposure dose towards target value(s).Alternatively or additionally, it may be efficient to utilize afeed-forward arrangement using one or more sensors that are alreadypresent in the substrate holder such as a transmission image sensor(TIS), a spot sensor and an integrated lens interferometer at scanner(ILIAS). Alternatively or additionally, the computer may calculate theappropriate correction(s) based on an abstract mathematical model of theprojection system and immersion liquid. An advantage of the abovearrangements is that they explicitly take into account the physicalinfluence of each property of the immersion liquid. In the examplesdescribed, the absorptivity of the liquid is recognized to besignificant predominantly in relation to exposure dose, while therefractive index profile is recognized to be significant in relation tofocus. Other physical properties may be treated in an analogous way. Forexample, one or dynamic effects linked with motion of the immersionliquid may also affect focus, exposure dose and/or other performancerelated features of the projection apparatus. These one or more effectsmay also be tackled via computer modeling using a similar algorithm asused to model the influence of liquid absorptivity and/or refractiveindex.

One or more optical properties of the liquid in the space may also bevaried by changing the geometry of the liquid. FIG. 10 shows anembodiment wherein the thickness of the liquid (as measured in adirection parallel to the axis of the final element of the projectionsystem) is varied. In this embodiment, a liquid geometry controller 19coordinates the operation of a liquid pressure controller 31 and asecond-component pressure controller 21. The space between the finalelement of the projection system and the substrate is filled with aliquid 12 and a second component 25, which may be a gas such as air. Theliquid and the second component may be constrained within the space byan upper seal member 17 and the contact-less seal 14. The thickness ofthe liquid, meaning the thickness of the liquid 12, is governed by therelative pressures of the liquid 12 and the second component 25,controlled in turn by the liquid pressure controller 31 andsecond-component pressure controller 21. The second component 25 neednot be a gas and may be chosen to be a liquid with a differentcomposition to the first. The relative amounts of the two componentscontained in the space between the final element of the projectionsystem PL and the substrate W may be manipulated to control the positionof the interface between the two and therefore one or more opticalproperties such as spherical aberration.

In an alternative or additional operational mode, the liquid pressurecontroller 31 may be operated independently to control the pressure ofthe liquid 12 and/or any flow of liquid in the space.

FIGS. 11 and 12 show embodiments wherein a pellicle 27 (e.g. a foil ofsolid transparent material such as glass) is provided as an interface tothe liquid in the space on a side of the liquid nearer the final elementof the projection system PL. The pellicle may be laterally unconstrained(FIG. 11) in which case, in an arrangement such as that shown in FIG.10, a planar interface is achieved, the pellicle acting to improve theoptical smoothness of the interface and reduce unwanted scattering.

Alternatively, as shown in FIG. 12, the pellicle may be formed from amaterial that can be deformed and be constrained in such a way that animbalance of pressure on either side of the pellicle causes deformation.In FIG. 12, a concave deformation is formed due to an overpressure inthe liquid 12. As a further variation, the thickness and material of thepellicle 27 may be adjusted to provide further image manipulation.

Further possible variations include non-symmetrical deformation ofeither or both of the predominant interfaces to the liquid 12, such asby tilting one with respect to the other. In the arrangement in FIG. 11,for example, a device may be provided to tilt the pellicle 27.

The above embodiments have shown the liquid in the space formed fromimmersion liquid. However, the space may be anywhere in the beam path.As an example, FIG. 13 shows an alternative embodiment wherein theliquid 12 is constrained between two pellicles 35 and 37. The shape ofthe liquid formed in this way may be varied by adjusting the pressure ofthe liquid 12 via an inlet 33. Either or both of the pellicles 35 and 37may be arranged to be flexible or rigid. A tuner may used to tune theoptical property by, for example, configuring the shape of the liquid bycontrolling pressure and/or the shape of the pellicle(s).

Further, the final element of the projection system PL may consist of aplane parallel plate 29. The mounting of this plate may be such that itcan move towards the substrate W, causing focus offset and/or sphericalaberration offset. In addition, the plate 29 may be tilted, which leadsto focus tilt and/or spherical aberration tilt. This may occur duringscanning movements where a pressure gradient in the liquid 12 isestablished over the surface of the plate 29 (this may depend on how theplate 29 is secured to the rest of the projection system PL). Focus tiltmay cause focus drilling (FLEX) and this may be manipulated bydeliberately controlling the tilt of the plate 29. On the other hand,spherical aberration offset may be manipulated by controlling theoverpressure of the liquid in the space, which affects the position ofthe plate 29 relative to the rest of the projection system.

In an embodiment, there is provided a lithographic projection apparatus,comprising: an illumination system configured to condition beam ofradiation; a support structure configured to hold a patterning device,the patterning device configured to pattern the beam of radiationaccording to a desired pattern; a substrate table configured to hold asubstrate; a projection system configured to project the patterned beamonto a target portion of the substrate; a liquid supply systemconfigured to supply a liquid to a space through which the beam ofradiation passes, the liquid having an optical property that can betuned; and a tuner configured tune the optical property.

In an embodiment, the space is located between the projection system andthe substrate. In an embodiment, the tuner is arranged to controlspatial dependence of the optical property of liquid in the space. In anembodiment, the tuner is arranged to provide and control a time-varyingoptical property of liquid in the space. In an embodiment, the tunercomprises a liquid temperature controller configured to control atemperature, and thereby one or more properties including the refractiveindex, absorptivity, or both, of liquid in the space. In an embodiment,the temperature controller comprises one or more heat exchangers,configured to establish one or more homogeneous or non-uniformtemperature profiles within the liquid in the space. In an embodiment,the one or more heat exchangers are arranged to add heat to or removeheat from, but not exchange liquid with, the liquid in the space. In anembodiment, the one or more heat exchangers are arranged to add heat toor remove heat from, and exchange temperature conditioned liquid with,the liquid in the space. In an embodiment, the one or more heatexchangers are coupled with the liquid supply system to effect theexchange of temperature conditioned liquid. In an embodiment, thetemperature controller comprises a plurality of independent heatexchangers arranged at different heights, radii, angles, or anycombination of the foregoing, relative to an axis lying in a planesubstantially parallel to the substrate. In an embodiment, the heatexchangers are arranged to add heat to or remove heat from, but notexchange liquid with, the liquid in the space. In an embodiment, theheat exchangers are arranged to add heat to or remove heat from, andexchange temperature conditioned liquid with, the liquid in the space.In an embodiment, the one or more heat exchangers are coupled with theliquid supply system to effect the exchange of temperature conditionedliquid. In an embodiment, the tuner comprises a liquid pressurecontroller configured to control the pressure, and thereby one or moreproperties including the refractive index, absorptivity, or both, ofliquid in the space. In an embodiment, the tuner comprises a liquidgeometry controller configured to control a shape of the liquid. In anembodiment, the liquid geometry controller is configured to control athickness of the liquid in a direction substantially parallel to theaxis of a final element of the projection system. In an embodiment, thetuner comprises a liquid composition controller configured to controlthe composition, and thereby one or more properties including therefractive index, absorptivity, or both, of the liquid in the space. Inan embodiment, the liquid composition controller comprises one or moreparticle exchangers configured to add impurity ions to liquid in thespace, remove impurity ions from liquid in the space, or both. In anembodiment, the liquid composition controller is arranged to replace afirst liquid in the space with a second liquid in the space, the secondliquid having a composition different from that of the first liquid. Inan embodiment, the first liquid or the second liquid may be formed ofone or more of the following: water, ethanol, acetone and benzoate. Inan embodiment, the apparatus further comprises one or more liquidsensors configured to measure, as a function of position, time, or both,a property of the liquid in the space including any one or more of thefollowing: temperature, pressure, boundary geometry, composition,refractive index and absorptivity. In an embodiment, the apparatuscomprises a device configured to correct a focus of the apparatus as afunction of the refractive index profile of the liquid in the space, asmeasured by the one or more liquid sensors. In an embodiment, theapparatus comprises a device configured to correct an exposure dose ofthe apparatus as a function of the absorptivity profile of the liquid inthe space, as measured by the one or more liquid sensors. In anembodiment, the tuner is arranged to create an optical effect includingspherical aberration, field curvature, or both. In an embodiment, thetuner comprises a computer controller configured to calculate a requiredsize of correction to one or more optical properties of the projectionsystem, the liquid, or both, based on a measured property. In anembodiment, the space with liquid therein forms a liquid lens. In anembodiment, the space is positioned such that the beam of radiation thatpasses therethrough has been patterned by the patterning device andtransmits the patterned beam from the projection system to thesubstrate.

In an embodiment, there is provided a device manufacturing method,comprising: providing a liquid in a space through which a beam ofradiation passes; tuning an optical property of the liquid in the space;and projecting the beam of radiation as patterned by a patterning deviceonto a target portion of a substrate.

In an embodiment, the space is between the substrate and a projectionsystem used to project the patterned beam. In an embodiment, tuningcomprises controlling spatial dependence of the optical property ofliquid in the space. In an embodiment, tuning comprises providing andcontrolling a time-varying optical property of liquid in the space. Inan embodiment, tuning comprises controlling a temperature, and therebyone or more properties including the refractive index, absorptivity, orboth, of liquid in the space. In an embodiment, controlling thetemperature comprises establishing one or more homogeneous ornon-uniform temperature profiles within the liquid in the space. In anembodiment, controlling the temperature comprises adding heat to orremoving heat from, but not exchanging liquid with, the liquid in thespace. In an embodiment, controlling the temperature comprises addingheat to or removing heat from, and exchanging temperature conditionedliquid with, the liquid in the space. In an embodiment, controlling thetemperature comprises establishing homogeneous or non-uniformtemperature profiles within the liquid in the space at differentheights, radii, angles, or any combination of the foregoing relative toan axis lying in a plane substantially parallel to the substrate. In anembodiment, controlling the temperature comprises adding heat to orremoving heat from, but not exchanging liquid with, the liquid in thespace. In an embodiment, controlling the temperature comprises addingheat to or removing heat from, and exchanging temperature conditionedliquid with, the liquid in the space. In an embodiment, tuning comprisescontrolling the pressure, and thereby one or more properties includingthe refractive index, absorptivity, or both, of liquid in the space. Inan embodiment, tuning comprises controlling a shape of the liquid in thespace. In an embodiment, controlling the shape comprises controlling athickness of the liquid in the space in a direction substantiallyparallel to the axis of a final element of a projection system used toproject the patterned beam. In an embodiment, tuning comprisescontrolling the composition, and thereby one or more propertiesincluding the refractive index, absorptivity, or both, of liquid in thespace. In an embodiment, controlling the composition comprises addingimpurity ions to liquid in the space, removing impurity ions from liquidin the space, or both. In an embodiment, controlling the compositioncomprises replacing a first liquid in the space with a second liquid inthe space, the second liquid having a composition different from that ofthe first liquid. In an embodiment, the first liquid or the secondliquid may be formed of one or more of the following: water, ethanol,acetone and benzoate. In an embodiment, the method further comprisesmeasuring, as a function of position, time, or both, a property ofliquid in the space including any one or more of the following:temperature, pressure, boundary geometry, composition, refractive indexand absorptivity. In an embodiment, the method comprises correcting afocus as a function of the refractive index profile of liquid in thespace, based on the measured property. In an embodiment, the methodcomprises correcting an exposure dose as a function of the absorptivityprofile of liquid in the space, based on the measured property. In anembodiment, tuning comprises creating an optical effect includingspherical aberration, field curvature, or both. In an embodiment, tuningcomprises calculating a required size of correction to one or moreoptical properties of a projection system used to project the patternedbeam, the liquid, or both, based on a measured property. In anembodiment, the space with the liquid therein forms a liquid lens. In anembodiment, the space is positioned such that the beam of radiation thatpasses therethrough has been patterned by the patterning device andtransmits the patterned beam from a projection system to the substrate.

In an embodiment, there is provided a lithographic projection apparatuscomprising: an illumination system configured to condition beam ofradiation; a support structure configured to hold a patterning device,the patterning device configured to pattern the beam of radiationaccording to a desired pattern; a substrate table configured to hold asubstrate; a projection system configured to project the patterned beamonto a target portion of the substrate; a lens formed from a liquid andhaving an optical property that can be tuned; and a tuner configuredtune the optical property.

In an embodiment, the tuner is arranged to control spatial dependence ofthe optical property of the liquid lens. In an embodiment, the tuner isarranged to provide and control a time-varying optical property of theliquid lens. In an embodiment, the tuner comprises a liquid temperaturecontroller configured to control a temperature, and thereby one or moreproperties including the refractive index, absorptivity, or both, of theliquid forming the liquid lens. In an embodiment, the temperaturecontroller comprises one or more heat exchangers, configured toestablish one or more homogeneous or non-uniform temperature profileswithin the liquid forming the liquid lens. In an embodiment, thetemperature controller comprises a plurality of independent heatexchangers arranged at different heights, radii, angles, or anycombination of the foregoing, relative to an axis lying in a planesubstantially parallel to the substrate. In an embodiment, the tunercomprises a liquid pressure controller configured to control thepressure, and thereby one or more properties including the refractiveindex, absorptivity, or both, of the liquid forming the liquid lens. Inan embodiment, the tuner comprises a liquid geometry controllerconfigured to control a shape of the liquid lens. In an embodiment, theliquid geometry controller is configured to control a thickness of theliquid lens in a direction substantially parallel to the axis of a finalelement of the projection system. In an embodiment, the tuner comprisesa liquid composition controller configured to control the composition,and thereby one or more properties including the refractive index,absorptivity, or both, of the liquid forming the liquid lens. In anembodiment, the liquid composition controller comprises one or moreparticle exchangers configured to add impurity ions to the liquidforming the liquid lens, remove impurity ions from the liquid formingthe liquid lens, or both. In an embodiment, the liquid compositioncontroller is arranged to replace a first liquid forming the liquid lenswith a second liquid forming the liquid lens, the second liquid having acomposition different from that of the first liquid. In an embodiment,the apparatus further comprises one or more liquid sensors configured tomeasure, as a function of position, time, or both, a property of theliquid forming the liquid lens including any one or more of thefollowing: temperature, pressure, boundary geometry, composition,refractive index and absorptivity. In an embodiment, the apparatuscomprises a device configured to correct a focus of the apparatus as afunction of the refractive index profile of the liquid forming theliquid lens, as measured by the one or more liquid sensors. In anembodiment, the apparatus comprises a device configured to correct anexposure dose of the apparatus as a function of the absorptivity profileof the liquid forming the liquid lens, as measured by the one or moreliquid sensors. In an embodiment, the tuner is arranged to create anoptical effect including spherical aberration, field curvature, or both.In an embodiment, the tuner comprises a computer controller configuredto calculate a required size of correction to one or more opticalproperties of the projection system, the liquid, or both, based on ameasured property.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. The description is not intended to limit theinvention.

1. A lithographic projection apparatus, comprising: an illumination system configured to condition beam of radiation; a support structure configured to hold a patterning device, the patterning device configured to pattern the beam of radiation according to a desired pattern; a substrate table configured to hold a substrate; a projection system configured to project the patterned beam onto a target portion of the substrate; a liquid supply system configured to supply a liquid to a space through which the beam of radiation passes, the liquid having an optical property that can be tuned; and a tuner configured tune the optical property.
 2. The apparatus according to claim 1, wherein the tuner is arranged to control spatial dependence of the optical property of liquid in the space.
 3. The apparatus according to claim 1, wherein the tuner is arranged to provide and control a time-varying optical property of liquid in the space.
 4. The apparatus according to claim 1, wherein the tuner comprises a liquid temperature controller configured to control a temperature, and thereby one or more properties including the refractive index, absorptivity, or both, of liquid in the space.
 5. The apparatus according to claim 4, wherein the temperature controller comprises one or more heat exchangers, configured to establish one or more homogeneous or non-uniform temperature profiles within the liquid in the space.
 6. The apparatus according to claim 4, wherein the temperature controller comprises a plurality of independent heat exchangers arranged at different heights, radii, angles, or any combination of the foregoing, relative to an axis lying in a plane substantially parallel to the substrate.
 7. The apparatus according to claim 1, wherein the tuner comprises a liquid pressure controller configured to control the pressure, and thereby one or more properties including the refractive index, absorptivity, or both, of liquid in the space.
 8. The apparatus according to claim 1, wherein the tuner comprises a liquid geometry controller configured to control a shape of the liquid.
 9. The apparatus according to claim 8, wherein the liquid geometry controller is configured to control a thickness of the liquid in a direction substantially parallel to the axis of a final element of the projection system.
 10. The apparatus according to claim 1, wherein the tuner comprises a liquid composition controller configured to control the composition, and thereby one or more properties including the refractive index, absorptivity, or both, of the liquid in the space.
 11. The apparatus according to claim 10, wherein the liquid composition controller comprises one or more particle exchangers configured to add impurity ions to liquid in the space, remove impurity ions from liquid in the space, or both.
 12. The apparatus according to claim 10, wherein the liquid composition controller is arranged to replace a first liquid in the space with a second liquid in the space, the second liquid having a composition different from that of the first liquid.
 13. The apparatus according to claim 12, wherein the first liquid or the second liquid may be formed of one or more of the following: water, ethanol, acetone and benzoate.
 14. The apparatus according to claim 1, further comprising one or more liquid sensors configured to measure, as a function of position, time, or both, a property of the liquid in the space including any one or more of the following: temperature, pressure, boundary geometry, composition, refractive index and absorptivity.
 15. The apparatus according to claim 14, comprising a device configured to correct a focus of the apparatus as a function of the refractive index profile of the liquid in the space, as measured by the one or more liquid sensors.
 16. The apparatus according to claim 14, comprising a device configured to correct an exposure dose of the apparatus as a function of the absorptivity profile of the liquid in the space, as measured by the one or more liquid sensors.
 17. The apparatus according to claim 1, wherein the tuner is arranged to create an optical effect including spherical aberration, field curvature, or both.
 18. The apparatus according to claim 1, wherein the tuner comprises a computer controller configured to calculate a required size of correction to one or more optical properties of the projection system, the liquid, or both, based on a measured property.
 19. The apparatus according to claim 1, wherein the space with liquid therein forms a liquid lens.
 20. A lithographic projection apparatus comprising: an illumination system configured to condition beam of radiation; a support structure configured to hold a patterning device, the patterning device configured to pattern the beam of radiation according to a desired pattern; a substrate table configured to hold a substrate; a projection system configured to project the patterned beam onto a target portion of the substrate; a lens formed from a liquid and having an optical property that can be tuned; and a tuner configured tune the optical property. 